Treatment of hydrocarbon oil



1936- c. D. LOWRY, JR.. El AL 2,064,842

TREATMENT OF HYDROCARBON OIL Filed Feb. 29,1932 2 Sheets-Sheet 1 CONDENSER FURNACE RECEIVER PUMP PRIR F INS Mme-R FURNACE SEPnRRroR FOR nnamnnca+ our-ma COMPRE58OR HG INVENTORS CHARLES D. LOWRY JR.

FELIX J. SKOWRONSKI BY z c. D. LOWRY, JR., El AL 2,054,842

TREATMENT OF HYDROCARBON OIL I Dec. 22, 1936.

Filed Feb. 29, 1952 2 Sheets-Sheet 2 rmnorwoa FURNACE I CRACKING I02 STOCK PUMP FOR PH RBI-F4 N6 PURI F I E R SEPRRHTOR MIXER 5 Oz SOLUTION FURNACE RROMRTICS OLEFI 9| RECEIVER P ran nnomnrlcs mm 01. us

FIG. 2 INVENTORS CHARLES D. LOWRY JR. FELIX J. SKOWRONSKI ATTOR E Y s'rss TREATMENT OF HYDROCON OIL Charles D. Lcwry, J12, and Felix J. Skowronski, Chicago, 111., assignors, by mesne assignments, to'Universal Oil Products Company, Chicago, 111., a corporation of Delaware Application February 29, 1932, Serial No. 595,708

13 Claims.

This invention relates more particularly to the treatment of lower boiling cracked distillates to increase their anti-knock value. I

More specifically the invention has reference 5 to a treatment-whereby the percentage of arom'atic and unsaturated compounds in cracked gasolines is increased to the greatest possible extent consistent with the production of a motor fuel having high anti-knock characteristics and at the same time free from objectionable prop' erties which sometimes are inherent in hydrocarbon mixtures of this character.

The naphthas or pressure distillates produced by the intensive heat treatment of heavy hydrocarbon oil mixtures such as topped crudes and heavy distillates therefrom contain higher percentages of olefins, naphthenes and aromatics" than fractions of corresponding boiling point range produced by the straight run distillation of the same crude petroleums, and the classes of hydrocarbon compounds mentioned add valuable properties to the gasoline fractions on account of their slow burning tendencies as comparedwith saturated or paraflinic hydrocarbons of similar boiling point. However, it is not practical commercially to increase the content of these constituents above a certain point in ordinary cracking operations on account of the formation on the one hand of increasingly large amounts of.

on the other hand of heavy polymerized substances typified by tars and coke. 13y subjecting cracked naphthas or gasolines to recracking' or reforming operations notable improvements in 35 knock rating can be obtained by suitable control to a point above that possible bythe use of pre- 7 viously known processes.

In one specific embodiment the invention com- 45 prises subjecting petroleum naphthas containing substantial amounts of gasoline boiling fractions to the action of liquid sulfur dioxide to separate said naphthas into a fraction of a predominantly aromatic and unsaturated character and a frac- 50 tion of a predominantlyparaflinic character, re-

moving sulfur dioxide from the former fraction and recovering motor fuel fractions of high antiknock value, subjecting the parafilnic fraction to conversion conditions of temperature and pres- 5 sure, further subjecting the condensed overhead gas and highly unsaturated hydrocarbons and low-boiling products from the conversion treatment to separation by means of liquid sulfur di oxide and continuing the operations until a motor fuelof desired anti-knock value is obtained.

tion of liquid sulphur dioxide, returning the 15 parafilnic fraction to the heating zone of the cracking process for further conversion, removing the sulfur dioxide from the aromatic fraction and recovering the latter. I

The attached drawings show diagrammatically in side elevation two forms of. apparatus in which the process may be carried out.

Fig. 1 shows an arrangement of apparatus suitable for the treatment of naphthas according to the first specific embodiment given, and

Fig. 2 shows a plant of somewhat more complex design in which heavier oils may be cracked and the naphtha subjected to treatment with liquid sulfur dioxide .to produce aromatic fractions for use as motor fuel and parafilnic fractions suitable for further conversion, according to the second specific embodiment given.

Referring to Fig. 1, naphthas containing substantial percentages of gasoline boiling fractions may be introduced to the system through a supply line I,- containing control valve 2, and leading to a 'feed pump 3 which in turn discharges to a. line 4, containing a control valve 5. Line l may receive a portion of the end products ofthe process which are cycled for further treatment from 40 a line 60, as will be later described.

Line 4 joins a line l8 supplying liquid sulfur dioxide in regulated amount, the mixture of oil and solvent passing through a line 6, containing control valve 1, to a mixer 8 which may be supplied with baflling devices to insure thorough contact and obtain maximum solvent action of the liquid sulfur dioxide. The solution of aro-' matic and unsaturated hydrocarbons in the sulfur dioxide along with the insoluble paraffinic hydro- 5o carbons may be discharged together through a line 9, containing a control valve l0. to a separator l I, still under pressure sufiicient toprevent. any substantial vaporization of the liquid sulfur dioxide. The actual pressure employed up to 66 and through the separator will depend upon whether the treatments are conducted at rela tively low temperatures obtainable by refrigeration or whether ordinary atmospheric temperatures are employed in which case pressures above the corresponding boiling points of liquid sulfur dioxide will be necessary. The actual choice or temperature and pressure conditions will depend upon a number of factors and the invention cornprises the use of anyconditions found necessary to eficient operation.

Separator ii is preferably of a capacity to permit efficient separation of insoluble paraffinic hydrocarbons from the solution of aromatic and unsaturated hydrocarbons in liquid sulfur dioxide. The solution, being of higher specific gravity than the insoluble oils, may be withdrawn from the bottom of the separator through a line l2, containing a control valve I13, to an intermediate receiver is in which the pressure is preferably reduced and the temperature raised if necessary until the best conditions are obtained for the substantially complete vaporization of the sulfur dioxide to leave a hydrocarbon residue of a highly aromatic and unsaturated character.

The sulfur dioxide evolved as a gas or vapor may require some purification from hydrocarbon oil vapors prior to their recompression to produce liquid sulfur diomde for further use and the hydrocarbons separated may also require a limited treatment of some character to' remove dissolved sulfur dioxide. However, the general character of such steps is Well known and needs no special description at this point, the description being given on the assumption that such steps have been employed though no means for accomplishing them is shown in the drawings for the sake of avoiding undue complexity.

The sulfur dioxide evolved from receiver M as a gas is then recompressed andliquefied, being passed through line l5, containing control valve I 5,110 a suitably designedcompressor ll from which it is pumped as a liquid (after absorption of the heat .of compression) through line it, containing control valve IQ, for further use as a solvent in the cycle already described. The disposition of the hydrocarbons separating in receiver it will be hereinafter described.

The insoluble paraffinic hydrocarbon oil fraction is indicated as being released from the upper portion of separator H throughline 23, containing control valve 2 I, and again it is assumed that suitable steps will be taken for the removal of any dissolved sulfur dioxide prior to the admission of the fractions to the conversion step. Thus, a pump 22 receives the portions of the original naphtha which have the lowest antiknock value on account of their generally par-.

than those employed when heavier charging oils are cracked owing to the greater volatility and heat stability of the lighter stocks. Thus, temperatures may be employed ranging from approximately -950 to '1100 .F. and pressures as high as 500. or 600 pounds per square inch or higher to obtain cracking conditions of suificient aoeaeae intensity to insure the desired degree oi decom position. The products from the heating ell merit may be discharged through a line 2s, containing a control valve and enter an enlarged zone ill in which decomposition reactions are allowed to progress to any desired degree without further. addition of heat, the reaction cha l-- ber being preferably well lagged to reduce radiation heat losses to a practical minimum.

The mixture of conversion products from chamber 35 may be discharged in toto through line 32, containing control valve 33 leading from the bottom of the chamber to a vaporizer 3 which is preferably maintained at a somewhat lower pressure so that the non-vaporized liquids separating at this point may be only those of a tarry or pitchy character unsuited to further conversion treatment, these being preferably withdrawn and rejected from the process through a line 35, containing a control valve 36.

The vapors from vaporizer 3% may be'passed to a fractionator by way of vapor line 3?, containing control valve 38 and line 39, containing control valve ili formed by the junction of line 37 with line M to be presently described. In fractionator M conditions may be so maintained that overhead fractions of substantially gasoline boiling range are evolved'along with fixed gases, the mixture being passed through line i'i, containing control valve 48, through condenser 39 in which liquefiable constituents of the mixture are condensed and then through line 5%, containing control valve St, to a receiver 52 in which fixed gases are separated from liquids, the former being released at a controlled rate through gas line 53, containing control valve 5 3 and the latter removed to storage through line 55, con- ;taining control valve 56 when they'are of proper quality.

Reflux condensates from fractlonator ll of higher boiling range than is desired in finished gasoline from the process will be conducted through a line d2, containing control valve cc,

to a recycle pump M from whence they are dis charged through line 45, containing control valve 36 to the conversion zone as already described.

In the event that the anti-knock value of the liquid in receiver 52 is not as high as desired, a portion or all of the liquid may be reprocessed. Thus, a recirculating pump 59 may take suction on the liquid in receiver 52 through a. line 5?, containing a control valve 58, and discharge same by way of line 60, containing control valve 6!, to line 4 as already described.

The mixture of aromatic and olefinic hydrocarbons separated from the sulfur diomde solution in receiver Id may be passed through a line 62, containing a control valve63, to a pump 64 which discharges the mixture through a line 65, containing control valve 66, through a heating element 61 disposed to receive heat from a furnace 68. Heat is preferably supplied at this point to accomplish at least the vaporization of those compounds of gasoline boiling point range so that the heated liquids discharged into fractionator M by way of line 69, control valve Hi, and line 39 and control valve d0 may be fractionated into a high antiknock overhead fraction and reflux condensates which may be further converted to produce more accesses cyclic character of the process is evident, the

- method of operation being such that from a naphtha of any character a high yield of antiknock value motor fuel may be obtained in a particularly efllcient and economicalmanner.

Referring to Fig. 2, hydrocarbon oils to be treated may be admitted to the system through a feed line "H, containing a control valve I02,

and discharged by a pump I03 through. a line I04, containing a control valve I05, into and through a heating element I 06 disposed to receive heat from a furnace I01, line I00 receiving cycle stocks from lines I53 and I95 as will presently appear.

The oils best suited to treatment in a plant arrangement of this character are the heavy charging oils which are ordinarily charged to commercial cracking processes for the production of gasoline and may comprise heavy uncracked petroleum fractions such as residua or heavy distillates or in some cases cracked residua or intermediate cycle stocks. The temperature and pressure conditions employed will be as a general rule less severe, temperatures ranging from approximately 875 to 935 F. and pressures of from 100 to 300 pounds per square inch comprising the usual conditions. The best conditions for any particular charging oil will usually be a matter of trial, the amount of cycling of the various intermediate products of the process having a determining effect.

Products from the heating element may be passed through a transfer line I08, containing a control valve I09, and be admitted to a reaction chamber. H0 in which the conversionreactions initiated and partly completed in the heating element may be allowed to progress to any desired point,.such a chamber being preferably well insulated to conserve heat units necessary for continuance of the endothermic conversion reactions.

While reaction chamber I I0 is shown as one to which the heating element products are admitted to the top and totally discharged through line III at the bottom, this feature is not necessarily peculiar to the present process but other types of -reaction chambers may be employed or, if advantageous for any purpose, the reaction zone may be entirely omitted. Similarly, the pressure maintained in the reaction zone shown may be substantially the same as that obtaining at the exit of the heating element, or may be reduced.

- The products from the reaction chamber, both vaporous and liquid, may be passed through valve I I2 in line II I and enter a chamber H3 under considerably reduced pressure, inthe neighborhood of to 100 pounds per square inch, and

ing aplurality of intermediate fractions in addition to overhead gasoline fractions of desired boiling point range. By suitable control of cracking conditions in the preceding. unit the vapors passing overhead from the fractionator through line I I9 and valve I20 may be of a character cor responding to'a high knock rating such as 80 octane number or thereabouts, the control of this property residing somewhat in the possibility of producing fractions of boiling range corresponding to maximum octane number at this point irrespective of yields. The vapors then follow the ordinary course of condensation by condenser I2I, the cooled fixed gases and gasoline fractions passing through'run-down line I22 and valve I23 to a receiver I24, which is provided with the customary gas release line I25, containing control valve I26, and a liquid draw line I21, containing control valve I28. The liquid fractions thus removed from the primary stage of the process may be reserved for blending with secondary products, as will be later described.

Heavy reflux condensates accumulating in the bottom of fractionator I I8 may be either returned to the heating element of thecracking zone for further conversion or passed directly to :the liquid sulfur dioxide extraction stage. In either event they may be withdrawn from the fractionator.

through line I 34, containing control valve I35.

or similar lines, and these fractions pumped by pump I30. through line I31, containing control valve I39,-into line I40 and thence to the sulfur dioxide mixer I. A portion or all of the end product liquids may also be passed to pump I 96 from receiver I24 through line I21, containing control valve I28. In this way there is offered a control 'of boiling point range of the fractionssubiected to the sulfur dioxide treatment; The

liquid sulfur dioxide treating plant consists, as

shown in the drawings, of a mixer I and a separator I49, though a. commercial treating plant of this character would necessarily involve a considerably more complex arrangement of apparatus, the simple set-up being shown as sufficient for the present purpose.

Liquid sulfur dioxide, or the gaseous phase of the same, may be admitted to line I42 from some ently described, and drawn through valve I03 by a compressor I. In case gaseous S02 is fed to the compressor it must have sumcient capacity to liquefy the gas and discharge the same through line I65, containing control valve I46, leading to the mixer. In this case also, cooling means may need to be interposed in line I to absorb the heat of compression, though these means are not indicated in the drawings.

The proportions of liquid sulfur dioxide employed in respect to the amount of oil admitted in the mixer will depend upon the character of the hydrocarbon mixtures admitted in regard to their'content of aromatic, naphthenic and olefinic constituents and the temperature and pressure conditions-chosen for the treating operation. When the oils treated have a low solidifying point :they may be treated at relatively low temperatures so. that the pressure upon the mixer and the succeeding separator is relatively low, whereas if ordinary or superatmospheric temperatures 'are maintained, correspondingly increased pressures must be employed to maintain the sulfur dioxide in a liquid state. Mixer l li may contain any type of filling or loading material necessary for providing a tortuous path of flow and insure thorough contact of the oils with the solvent.

The mixer products comprising a solution of hydrocarbons of a predominantly aromatic and olefinic character in the liquid sulfur dioxide, and the insoluble liquids of a more distinctly parafinlc nature may then be passed through line i l'i, containing control valve t lt, into separator M9, in which substantially the same pressure is maintained which has been found to be necessary to prevent vaporization of the sulfur dioxide. In this separator the solution of oil in liquid sulfur dioxide will gradually settle to the bottom while undissolved fractions will rise to the top on account of differences in specific gravity. Separator Ida is again shown to represent any type of separating apparatus and Will usually be more complex than the simple tank shown.

At this point one of the important features of this invention is again to be noted, that is, that the more highly paraifinlc fraction is returned directly to the heating zone of the cracking process for further conversion while the suliur dioxide-soluble hydrocarbons are separately treated to produce high knock rating blending fluid and refiux condensates which are separately returned tothe cracking process. Thus,.intermediates from the cracking process containing components of lowest knock rating are continually re-subjected to conversion conditions to produce increased yields of anti-knock fractions, these SO -insoluble mixtures being taken through l ne I56, containing control valve I5I and discharged by pump !52 through line 953, containing control valve 95%, to combined feed line Hid. These fractions, which usually contain a certain amount of dissolved sulfur dioxide may be subiected to moderate heat treatment or alkaline washing, or both, to remove the traces of sulfur dioxide prior to the re-admission of the oils to the cracking zone, though means for efiecting this objecthave been omitted from the present drawings for purposes of simplification.

The solution of aromatics, olefins, etcetera, in liquid sulfur dioxide is removed from the bottom of the separator through a line H55, containing a'control valve I56, and passed to low pressure separator I57, wherefrom the liquid sulfur dioxide is vaporized and returned through line E58, containing control valve I58, to the suction side of compressor 6, as already indicated. Again,

with the object of avoiding unnecessary detail, separator l5! has been shown without any means for exterior heating to eifect the complete removal of sulfur dioxide from the hydrocarbon oils,

though such means usually have to be employed for this purpose. Furthermore, it may be necessaryto condense out volatile hydrocarbons fro-m the sulfur dioxide prior to its re-compresslon and liquefaction, and for a similar reason suchequipment has been omitted from the drawings.

The sulfur dioxide-soluble fraction is taken from separator-J51 by a pump- I62 through line i60 containing a control valve I6l, and dis-' charged through line I63, containing control valve I64, into and through a heating element ace-seas material suitable for blending with the lower boiling gasoline fractions from the first stage of the process. While the operation being described islimited to a particular type of vapor phase treatment, other vapor phase treatments may be used or the extracted liduidsqmay be refined in liquid phase by sulfuric acid and other reagents and revaporized. However, the vapor phase treatment to be presently described is particularly adapted to the treatment found to be necessary in suitably refining these oils and it will be given in essential detail.

Heated and vaporized oils may be passed from the tubular heating element through a transfer line itl, containing a control valve 868, and admitted to lower vapor space iill of vapor phase treater ill after the addition of regulated amountsof hydrochloric acid either in solution or as a, wet gas from line its, containing control valve ild. Vapor phase treater ill contains solid contact material of a metallic or adsorbent character in space H2, this material being supported upon a perforated false bottom I13. While the present description is confined to an up-fiow treatment with some accompanying fractionation, down-flow treatments may also be employed, in which case a greater burden is placed upon the succeeding fractionator.

Hydrochloric acid and solid contact materials,

particularly those of a metallic character, such as, for example, granulated zinc, copper or brass are effective for the more or less selective polymerization' of highly unsaturated gum-forming v hydrocarbons undesirable in a finished gasoline for obvious reasons. Some desulfurization may also be effected, depending upon the proportion of electro-negative metals, such as copper, in the contact mass, either in mechanical admixture or alloyed with electro-posltive metals. Heavy polymers and reaction products accumulating in" lower section ild of the vapor phase treater may be removed therefrom through a draw line I76, containing control valve ill and disposed of in the most advantageous manner. For example, the hydrocarbons may be separated, from any sludge reaction products and returned to the cracking unit and the sludge materials, comprising at times heavy metal chlorides, may be either wasted or returned to the contact mass after suitable purification.

Treated vapors accumulating in upper section Il5 of the. vapor phase treater may be conducted to afinal fractionator I80 through a line 518, containing a control valve H9, and subjected to fractionation to produce refined overhead fractions to be blended with the overhead fractions from the cracking unit. Owing to the highly aromatic character of these secondary overhead fractions, as evidenced by. their octane number, which is frequently as high as 100-120, they constitute a valuable product of the'proces's and are preferably blended with the primary cracked overhead fractions to produce a composite motor fuel of exceptionally high knock rating. Such vapors may be passed from the' fractlonator through a. line I8I,'containing a control valve I82, and condensed during passage through a condenser I83, the liquid fractions being passed through run-down line I 84, containing control valve I85, to receiver and separator I86, from which fixed gases may be released through a line I81, containing a control valve I88, and the liquids withdrawn through a line I89, containing a control valve I80, either, for direct blending with the primary cracking plant fractions or intermediate storage. The blending may be effected by passing cracked distillate from receiver :24 into line I8I through line I8I', having valve The reflux condensates from fractionator I80, constituting relatively heavy oils though still of a highly aromatic character, may be either cycled to the heating zone of the cracking plant or to the sulfur dioxide treating plant. These fractions are withdrawn from the fractionator through a line I9l, containing a control valve I92, and pumped by pump I93 through line' I94, containing control valve I95, to the junction of lines I95 and I91, the former leading to combined feed line I04 of cracking plant and the latter to line I32 leading ultimately to mixer The preferred disposal ofthese heavy fractions will be determined experimentally in most cases.

The foregoing plant hook-ups used in describing characteristic operations are capable of many modifications and, owing to the wide variety of charging stocks which can be cracked and treated in plants of this general character, specific examples of'results obtainable could be multiplied considerably. Two, however, will be sufiicient to show the merits and advantages of the process and cases will be taken involving the processing of (l) a naphtha produced from Pennsylvania crude oil, and (2) a heavy gas oil fraction produced in the primary distillation of a mixture of Mid-Continent and West Texas crude oils. .The'

- results obtainable in the first case may be by the operation of a plant of design generally similar to that shown in Fig. l and in the second case from a hook-up similar to Fig. 2.

The naphtha in the first case may contain approximately 85% of hydrocarbons boiling under 400 F., the raw gasoline produced by simple fractionation having the properties shown in column 1 while the corresponding properties of a gasoline produced by the application of the process has the properties shown in column 2.

Comparison of gasolines Gravity A. P. I-.... 6O 55 End point F 400 390 Octane number 45 75 The yield of gasoline from the naphtha may be reduced from approximately 85% to 83% by this treatment which is more than compensated for by the marked increase in anti-knock value.

The general properties of the charging oil which may be processed in a manner generally similar to that described in connection with Fig. 2 are indicated by its gravity of 30 A.-P. I. and its content of 5% of hydrocarbons boiling below 437 F. and 25% below 572 F. By 'the most economic cracking of this stock in a cracking unit generally similar in character to the primary unit shown in the drawings it is possible to produce a yield of 60% of gasoline having a final boiling point of 390-400 F. and an octane number of 65, with the concurrent production of 25% of 6 A. P. I. gravity fuel oil residuum and 15% by weight of fixed gases.

By combining a cracking unit with a sulfur dioxide treating unit and a vapor phase treater as described, the yield of gasoline overall may be increased to 78%, the residuum decreased to 13% and the gasloss to 9%, the gasoline having the same endpoint and substantially the same distillation curve, but an octane number of 90.

In operating to produce the improved yields and quality in the gasoline, 60% of 325 F. endpoint overhead stock may be condensed from the cracking plant fractionator, while 25% of a mixture of side cuts and bottom refluxes on a basis of the oil charged may be treated in the sulfur dioxide treating unit. Using two volumes of liquid sulfur dioxide to one ofoil in the treating plant under suitable conditions of temperature and pressure may cause an approximately equal split of these oils into paraflnic cycle stock returned to the heating element for further cracking and a mixture of aromatic hydrocarbons which, after refining by the vapor phase treatment indicated, may have the following properties:

The tabulated properties ofthe secondary or aromatic blending stock permit, therefore, its blending with the primary overhead gasoline to produce a finished gasoline having a knock rating of 90 octane number. For purposes of better comparison, the comparative data on the two types of operation are tabulated below, column 1 showing figures corresponding to ordinary cracking operation, and column 2 figures corresponding to the improved process of the present invention:

Gasoline yield 60 '18 Octane number 65 90 Residuum,-yield 25 13 Gas, yield 15 9 In operations of the general character under discussion the overall recycle ratio, including primary and secondary'refiuxes and sulfur dioxide-insoluble oils, may be considerably lower than in straight cracking operations, since the portions of the charging stock requiring more intensive decomposition are cracked selectively.

The foregoing specification, including the description of two operations and results obtainable therefrom, will be suificient for accurately defining the nature and scope of the invention, but since other modifications are possible with corresponding variations of results none of the preceding specification is to be construed as imposing undue limitations upon the broad scope of the invention. I

We claim as our invention:

1. A continuous process for converting a cracking stock into high octane number gasoline, comprising the steps of cracking the stock to form a cracked gasoline, separating the latter into a low boiling fraction and a high. boiling fraction, treating the high boiling fraction with liquid-S02, separating the ramnate and extract, removing the solvent therefrom, recycling the rafiinate by mixing it with the cracking stock entering the cycle, and blending said extract with said low boiling fraction to produce the high octane number gasoline.

, entirety of an ordinary cracking stock, containing both saturatedand unsaturated hydrocarbons, into a high octane number gasoline, coinprising cracking said stock to form a cracked gasoline, dividing the latter into a low boilingv fraction and a high boiling fraction, treating the high boiling fraction with liquid-S02, separating the rafiinate and extract, removing the solvent therefrom, blending said extract with saidv low boiling fraction to form a high octane number gasoline, mixing said rafiinate with cracking stock containing both saturated and unsaturated hydrocarbons, cracking the mixture so as to form a' cracked gasoline, subjecting the cracked gasoline to the appropriate sequence of process steps described above, and in like manner treating the successive raihnate resulting from continuing the process herein set forth..

4. A process for converting substantially the entirety of a cracked gasoline into a high octane number gasoline, comprising dividing the cracked gasoline into a low boiling fraction and a high boiling fraction, treating the high boiling fraction with liquid-S02, separating the raffinate and extract, removing the solvent therefrom, blending said extract with said low boiling fraction to form a high octane number gasoline, mixing said rafinate with v cracking stock containing bothsaturated and unsaturated hydrocarbons, crack-v ing the mixture so asto form a cracked gasoline, subjecting the latter to the foregoing sequence of steps described for the cracked gasoline, and in like manner treating the successive rafiinate resultingfrom continuing the process herein set forth. 5. A process for the production of a highly olefinic anti-knock motor fuel comprising cracking a hydrocarbon charging stock, separating a light cracked naphtha and a heavy cracked naphtha, contacting said heavy cracked naphtha with a selective solvent, separating a ramnate fraction and an extract fraction, removing solvent from each of said fractions, recycling at least a portion of the rafiinate to the cracking step and blending at least a portion of said light cracked naphtha and at least a portion of said extract.

6. A process for the production of anti-knock motor fuel which comprises subjecting a hydrocarbon oil'to cracking conditions of temperature and pressure, separating a light cracked naphtha and a heavy cracked naphtha, contacting said heavy cracked naphtha with a selective solvent to form a parafiinic fraction and an unsaturated fraction, removing solvent from each of said fractions, recycling at least a portion of the paraflinic fraction to the cracking step, and blending at least a portion of said light cracked naphtha aoeaeae and at least a portion of said unsaturated fraction.

7. The process as defined in claim 6 further characterized in that said hydrocarbon oil comprises an oil heavier than gasoline in addition to said portion of the parafiinic fraction recycled to the cracking step.

3. A process for producing anti-knock motor fuel from low boiling distillates of the character of gasoline and naphtha, which, comprises treating the distillate with liquid-S02 or like solvent separating the resultant raffinate and extract and removing solvent therefrom, combining the raidnate with a cracking stock, cracking the resultant mixture and blending gasoline boiling hydrocarbons thus formed with gasoline boiling portions of said extract.

9. ihe process as definedin claim 8 further characterized in that said cracking stock is a hydrocarbon oil heavier than said distillate.

10. A process for producing anti-knock motor fuel which comprises cracking a paramnic oil formed as hereinafter set forth, separating the resultant cracked gasoline into a low boiling fraction and a high boiling fraction, treating the latter with: liquid-S02 or like solvent, separating'the resultant raflinate and extract and removing solvent therefrom, supplying the raifinate to the cracking step as said parafiinic oil, and'blending said low boiling fraction "with gasoline boiling portions of said extract.

11. A process for producing anti-knock motor fuel which comprises cracking a hydrocarbon oil heavier than gasoline, separating the resultant cracked gasoline into .a low boiling fraction and a high boiling fraction, treating the latter with liquid-S02 or like solvent, separating the resultant rafi'i'nate and extract and removing solvent therefrom, recycling the ramnate to the cracking step for further cracking in' admixture with said hydrocarbon oil, and blending said low boiling fraction with gasoline boiling portions of said extract.

12. A process for producing anti-knock motor fuel from a petroleum-cracking stockwhich comprises cracking the stock, separating the resultant cracked gasoline into a low boiling fraction and a high boiling fraction, treating the latter with liquid-S02 or like solvent, separating the resultant raflinate and extract and removing solvent therefrom, recycling the raflinate to the cracking step for further cracking in admixture with said stock, and blending said low boiling fraction with gasoline boiling portions of said extract.

13. A process for producing anti-knock motor fuel from low boiling distillates of the character of gasoline and naphtha, which comprises treating the distillate with liquid-S02 or like solvent, separating the resultant raflinate and extract and removing solvent therefrom, cracking the ramnate and fractionating resultant cracked vapors in a fractionating zone, introducing the extract to the fractionating zone 'for' fractionation therein together with said cracked vapors, recycling reflux condensate from the fractionating zone to the cracking step for further cracking in admixture with the raflinate, and finally condensing the I gasoline vapors uncondensed in the fractionating CHARLES D. LOWRY, JR. FELIX I. sxownonsm. 

